I'm never quite sure if I am posting to the right forum with projects like this. I assume MELM or Dick will move the posting if it is in the wrong place. BTW, I wish we had a "camper mods" Forum.
...................................................................

This is a project I finished up this past week. It is not intended to be a “how-to-do-it” posting but rather a summary of what can be accomplished.

If you are the kind of guy who gets a real adrenaline rush out of using an electric drill, saw, hammer and other tools then sits back with pride and says, “By golly, I made that myself!”, then this posting is for you.

But, if you don’t like tools and the challenge of making something from nothing, and would rather just go buy it off the shelf; you most likely will not get the point of this posting.

The wife and I bought a 2009 Cedar Creek 34SATS fifth wheel trailer a few weeks back. The camper it replaced was a 2005 Prowler Regal 330FKDS. She jokingly commented the only reason I wanted a new trailer was because I had run out of things to change or make for the old one.

The Cedar Creek came with one 15,000 BTU air conditioner that is ducted to all living areas of the camper. We found out the first week that one A/C was not going to be enough to make this large of a camper comfortable in 90+ degree weather.

There was a 14” vent in the bedroom that had factory wiring and a brace for adding a second A/C.

After some thought, I decided that I wanted an A/C smaller than the typical 13,500 BTU units that most folks were installing.

My reasons for wanting a smaller unit providing around 6,000 BTUs and drawing about 600 watts at 120 volts were primarily related to our occasional camping in hot weather with no hook-ups. With the bedroom door closed so as to isolate it from the rest of the camper, we could run just the bedroom A/C off of a quite 1200 watt generator to cool the sleeping area. I could even run a smaller A/C from the 1,500 watt DC to AC inverter. Three deep cycle group 29 batteries would give me at least 4 hours of cold air – enough to cool down a hot bedroom during a camp ground’s generator quite hours so we could get to sleep.

Another plus would be the ability to run both A/C units when only a 30 amp hook-up was available. You see, 30 amps will handle 21,000 BTU’s of A/C, a TV and a microwave if you refrain from using electric hot water heating and switch the refrigerator to LPG mode. Of course, the DW needs to turn one of those items off to use her 1,500 watt hair dryer.

The lower noise level of a small unit also looked favorable. The noise from the ducted 15,000 BTU unit with the big fan can be annoying at times.

But there was a problem. Small RV air conditioners with the BTU and wattage rating I wanted were not available. I could special order a “PUP” A/C, but the cost was equal to a 13,500 BTU and it was still larger than I wanted.

So, I decided to make one. Nancy just shook her head – here we go on another project.

I started with a Samsung 6,000 BTU window air conditioner from Lowe’s. The end of season clearance price was just under $90. This particular A/C also had a digital control panel and a remote. I like gadgets like remotes.

The shop foreman where I have conducted my RV business for years gave me a 13,500 BTU Dometic Brisk Air unit that had burned out it’s compressor after the fan motor seized. The cover and metal base were in good condition. I bought a new mounting kit that included the inside piece. The install kit and gasket hit me up for a little less than $100.

Once the old Dometic Brisk Air unit was back at my workshop, I evacuated the refrigerant into a recovery bag for cleaning/recycling and completely gutted the entire assembly, leaving only the metal base pan.

I then disassembled the Samsung unit from its base and framework and re-mounted the evaporator into the old Brisk Air return air cabinet and reused the original Dometic condensation drain fixture under the Samsung evaporator.

The smaller Samsung fan assembly fit nicely into the old housing that pulls return air into the evaporator and blows cooled air down the square chute into the inside cover’s air box. It did require some trimming of plastic on the band saw and a few #10 stainless steel nuts and bolts.

I decided to open the Samsung system so that it was easier to handle relocation of the evaporator, compressor and condenser. This meant that I had to braze the lines back together, vacuum down the system and recharge with R22. I do have the license and equipment to legally do this. In retrospect, it was not necessary to open the Samsung system or the original Dometic system. Both can be handled as a closed system. The Dometic parts can then be taken to a Freon recovery capable recycling center for proper disposal. While R22 refrigerant is not believed to be as dangerous to the ozone as R12 was, it is being phased out and does require recovery. A 30# cylinder of R22 is now over $200. Thus, it is best to not open the system.

Mounting the Samsung condenser required some metal “L” brackets and a few shims to get it properly aligned. I also had to bend a piece of sheet metal into a “L” shape 6” wide and 12” long to close off one side of the return air duct due to the smaller evaporator.

I cut an opening for the digital control unit from the Samsung into the plastic inside air box unit. I had to splice in some longer wires, but other than that it was a rather simple process. The new mechanical Dometic fan speed control and thermostat that came with the install kit were not used.

Getting a large, heavy A/C onto the roof of a tall RV is a challenge. An old guy like me can’t just heft it over his shoulder and climb up the ladder. I ended up using an extension ladder set at an angle and made a trolley I could pull up the ladder with the A/C. It worked great.

Perhaps the most difficult part of the project was removing the 14” roof vent. Forest River must have used a gallon of sealant around the vent screws. It took forever to clean it off and get the ¼” head screws out.

The unit is now installed and performs fantastically. With the bedroom door closed and the outside temperature at 85 degrees F, the bedroom gets cold enough to hang meat. It is also extremely quite compared to a larger A/C. I also like the added feature of being able to control the unit with a remote from my side of the bed without needing to get up.

So, converting a window A/C to a rooftop RV A/C is not only possible, but economically practical provided you have some common tools and a junk roof top A/C unit with a good cover to use as a cabinet.

If you should decide to attempt the same project, I will be glad to offer any assistance I am able to by dropping me an e-mail or posting your questions here.

ABOVE - FRONT VIEW SHOWING EVAPORATOR FROM SAMSUNG MOUNTED IN OPEN RETURN AIR BOX OF RV A/C CABINET. NOTE ORIGINAL DOMETIC CONDENSATION DRAIN PAN (WHITE PLASTIC UNDER EVAPORATOR) AND SIDE PANELS. COVER GOES OVER SIDES TO CLOSE AIR BOX. ADDED PIECE OF SHEET METAL MENTIONED IN TEXT IS TO LEFT OF EVAPORATOR COIL.

ABOVE - MOUNTING OF SAMSUNG CONDENSER AND COMPRESSOR (SURE IS A LOT OF EXTRA ROOM!) OEM SAMSUNG COMPRESSOR MOUNTING STUDS, RUBBER ISOLATION MOUNTS AND NUTS WERE MOVED TO DOMETIC PAN.

ABOVE - RIGHT SIDE VIEW SHOWING FAN HOUSING DETAIL. NOTE "L" BRACKET ON CONDENSER. LARGE FLAT METAL PIECE IN CENTER PAN FLOOR IS NEW MOUNTING BRACKET NEEDED FOR SMALLER DIAMETER LONG BOLTS PROVIDED WITH INSTALL KIT. IT HAD TO BE DRILLED AND THREADED TO ACCEPT 7/16" BOLTS. PROTRUDING SCREWS WITH NUTS JUST HOLD IT IN PLACE.

ABOVE - VACUUMING THE OPEN SYSTEM DOWN TO REMOVE MOISTURE AND RECHARGING WITH R22. I ELECTED TO GIVE THE UNIT A LOW CHARGE SO THE COIL WAS AT 30 DEGREES WITH AIR TEMP AT 70 DEGREES. I WILL NEED TO KEEP AN EYE ON IT TO AVOID FREEZING THE COIL ON COOL DAYS, BUT WILL HAVE COLDER AIR ON HOT DAYS.

ABOVE - THIS IS THE CEILING AIR BOX WITH THE ORIGINAL SAMSUNG DIGITAL CONTROL UNIT INSTALLED. i SIMPLY CUT A HOLE WITH A SABER SAW, USED A FILE TO MAKE IT SQUARE AND GLUED IT IN WITH RTV. THE REMOTE CONTROL FOR THE A/C IS SHOWN AT THE BOTTOM OF THE AIR BOX.

ABOVE - HOW A 63 YEAR OLD MAN GETS A HEAVY A/C ONTO THE ROOF OF A TALL RV. A/C UNIT IS ON A PLYWOOD TROLLY WELL LUBRICATED SO IT SLIDES EASILY UP THE LADDER RAILS.

ABOVE - INSIDE AIR BOX WITH DIGITAL CONTROL. YOU CAN HARDLY HEAR THIS UNIT RUNNING! I'M STILL TRYING TO FIGURE OUT WHY IN THE HECK FOREST RIVER HAD TO MOUNT THE POWER ACCESS BOX ON THE OUTSIDE OF THE AIR BOX (NOTE PLASTIC BOX COVER TO RIGHT).

ABOVE - FRONT A/C UNIT ON ROOF IS THE CONVERTED UNIT. I HOPE I AM NOT TOO TALL TO GET THRU THE HAMPTON ROADS BRIDGE TUNNEL! WILL MEASURE TOTAL HEIGHT TODAY.

NICE JOB, Professor! I have a similar situation on my motorhome...one 13,500 btu ducted A/C. So far it's been ok for the hot weather, but there may come a time I wish to add the second A/C. I will definitely keep this post in mind.

For the average DIYer, I would rate your project right up there close to a 10 in difficulty, especially not having the knowledge to work with A/C refrigerants, but will keep it in mind. Again. NICE JOB!

zigzagrv wrote:NICE JOB, Professor! I have a similar situation on my motorhome...one 13,500 btu ducted A/C. So far it's been ok for the hot weather, but there may come a time I wish to add the second A/C. I will definitely keep this post in mind.

For the average DIYer, I would rate your project right up there close to a 10 in difficulty, especially not having the knowledge to work with A/C refrigerants, but will keep it in mind. Again. NICE JOB!

Thank you. I'll give it a 7 or 8 rather than a 10. Keep in mind you DO NOT need to open the refrigeration system on either the old or new unit. It all can be done with the systems sealed if you are careful about removing and moving the parts. The Samsung window AC had a very long, coiled cap tube and the copper line from the compressor to the evaporator could easily be pulled out another 3-4".

In my area, you can drop off old A/C units and refrigerators at the county transfer and recycling station. A licensed tech will then come in and evacuate/recover the CFC from the system. There is no charge for drop off. Check your area, it may offer the same. Also, if you can get an old unit from a RV dealer, they should be able to evacuate the system beforehand. One plus, the scrap aluminum and copper from the old units brings a good price at a recycling yard. The old evaporator and condensor can also make an excellent transmission cooler coil!

Posted By: Bumpyroad
on 09/29/08 11:23am

nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

Posted By: Dark Green HD Dmax
on 09/29/08 01:56pm

Kodos to U...Well Done! One bad thing now....the price of RV AC unit shells will SKYROCKET !!!!! & No more free used (scrap) units! If this catches on, the RV industry WILL figure an angle to get more profits from the retrofits...unless your redoing a unit you already have!

* This post was
edited 09/29/08 03:09pm by Dark Green HD Dmax *

Posted By: Dark Green HD Dmax
on 09/29/08 03:14pm

Bumpyroad wrote:nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

If you do your homework right & your attemting to redo a unit you already have...then you can save some big bucks!

Posted By: Bumpyroad
on 09/29/08 03:44pm

Dark Green HD Dmax wrote:

Bumpyroad wrote:nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

If you do your homework right & your attemting to redo a unit you already have...then you can save some big bucks!

IIRC, I didn't pay what I would consider to be "big bucks" for my second one.
bumpy

Posted By: Dark Green HD Dmax
on 09/29/08 04:01pm

Bumpyroad wrote:

Dark Green HD Dmax wrote:

Bumpyroad wrote:nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

If you do your homework right & your attemting to redo a unit you already have...then you can save some big bucks!

IIRC, I didn't pay what I would consider to be "big bucks" for my second one.
bumpy

I guess one persons big bucks is anothers small change. Personally had i seen this article 2 years ago, i would had seriously considered a retro fit for my 2nd unit. I spent $600.00+ on a coleman polar cub
& installed it myself. To me 600+ bucks is big bucks....or now about 5 diesel fillups.....but then thats about how many times i filled my truck up last year!

Posted By: Bumpyroad
on 09/29/08 04:03pm

Dark Green HD Dmax wrote:

Bumpyroad wrote:

Dark Green HD Dmax wrote:

Bumpyroad wrote:nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

If you do your homework right & your attemting to redo a unit you already have...then you can save some big bucks!

IIRC, I didn't pay what I would consider to be "big bucks" for my second one.
bumpy

I guess one persons big bucks is anothers small change. Personally had i seen this article 2 years ago, i would had seriously considered a retro fit for my 2nd unit. I spent $600.00+ on a coleman polar cub
& installed it myself. To me 600+ bucks is big bucks....or now about 5 diesel fillups.....but then thats about how many times i filled my truck up last year!

and how much would you have to pay for parts for the do it yourself jobby? I guess if you already had all the parts, shell of an old AC etc.
bumpy

Posted By: quabillion
on 09/29/08 04:31pm

Bumpyroad wrote:

and how much would you have to pay for parts for the do it yourself jobby? I guess if you already had all the parts, shell of an old AC etc.
bumpy

I could pull that off in about a days time,,, with only the *stuff* that I carry in my rig. But then again I am the type of gadget geek who would. Who else would carry around 90 pounds of dichlorodifluoromethane in the rig???

Great work there Professor!!

Do you have a running wattage measurement, post modification??

I spend every day of my life trying to understand that other people in this world do things differently than I do.

Posted By: Lost One
on 09/29/08 06:04pm

Good work Professor, the only thing I think I would have done since you had already evacuated the system would have been to get rid of the saddle tap (I know it was for evacuating) and brazed in a permanent one.

and how much would you have to pay for parts for the do it yourself jobby? I guess if you already had all the parts, shell of an old AC etc.
bumpy

You really don't have a clue why people do things like this, do you?

When I saw the thread title I could picture some one trying to clamp a window ac to the roof and duct the air down the roof opening. But seeing what you did I am impressed, great job.

Seeing the pictures did make me think about what would happen if he ac ever needed to be serviced once you sell it. I would love to see the look on the techs face when he pulled the cover off....

Posted By: DustyRoad
on 09/29/08 07:02pm

Interesting thread ... thanks!

Posted By: professor95
on 09/29/08 07:25pm

Bumpyroad wrote:nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

You're right, it is a lot of work to save a couple of hundred dollars at most. But, when you are a baby boomer on full retirement, including SSI, you measure things differently than when you were working full time (with no "spare" time ) and knocking down big bucks. What big bucks I did have stuffed in the mattress were soaked up buying the Cedar Creek and paying the sales tax.

Fortunately, the IRS does not consider the money I saved (rather than earned and spent) as taxable income.

Besides, it was fun and provided the stimilus to keep my mind exercised - not to mention my back hauling the thing up on the roof.

One man's work can be another man's pleasure. I waited 40 years to get out of the 7 a.m to 11 p.m. rat race so I could waste my time like this .

Posted By: professor95
on 09/29/08 07:29pm

Lost One wrote:Good work Professor, the only thing I think I would have done since you had already evacuated the system would have been to get rid of the saddle tap (I know it was for evacuating) and brazed in a permanent one.

I did. The photos just did not show them. I like to "sweep" a small cap tube system that has been open for more than a few minutes at least once to be sure no moisture is left behind that might freeze (I can no longer pull a full 29" of vacuum with my old pump). I put them in before the last purge and recharge. Apparently you have experienced how those little buggers will leak no matter how tight you twist the screws.

* This post was
edited 09/29/08 07:37pm by professor95 *

Posted By: Lost One
on 09/29/08 08:52pm

professor95 wrote: Apparently you have experienced how those little buggers will leak no matter how tight you twist the screws.

Ya, that and the little allen wrench they send that would rather twist than tighten the screw.

Sad part is if you go out on a service call and the customer tells you he has to have it filled all the time (I will only change it once) and you find one and want to remove it they never want to pay for it to fix it right.

Posted By: Bumpyroad
on 09/30/08 04:40am

itsalleasy wrote:

Bumpyroad wrote:

and how much would you have to pay for parts for the do it yourself jobby? I guess if you already had all the parts, shell of an old AC etc.
bumpy

You really don't have a clue why people do things like this, do you?

snip.

well, it sort of seems like professor95 had no real problem with my comment, although you evidently did.
bumpy

Posted By: Chris Bryant
on 09/30/08 06:46am

Nice job! A couple of comments...
A lot of times I will do something like this "just because I can"
It was interesting to see the relative size of the coils looked to be close to the 13.5K unit, which I would bet boosts the efficiency quite a bit.
The only concern I would have is with the condenser air- did you baffle it off inside the shroud so it cannot simply recirculate?

BTW: I am waiting for you to show us how to best use our Champion 3000w gensets in a permanent installation. My C46540 is sitting on ready just in case my Generac 4000, in my MH fails.

Floyd

Posted By: professor95
on 09/30/08 08:19am

Chris Bryant wrote:Nice job! A couple of comments...
A lot of times I will do something like this "just because I can"
It was interesting to see the relative size of the coils looked to be close to the 13.5K unit, which I would bet boosts the efficiency quite a bit.
The only concern I would have is with the condenser air- did you baffle it off inside the shroud so it cannot simply recirculate?

Air routing and baffeling is per the OEM Brisk Air system. Big air return in the front that is partitioned in the inside air box and a square cold air outlet that dumps out of the blower into the two ducted ports of the air box. Guess I should have made more photos showing the inside of the air box?

A far as coil size, the evaporator on the 6K unit was only slightly smaller, but the condenser was twice as large. The fan motor is much smaller (and quite!) and the compressor makes absolutely no desernable noise at all inside the RV. In fact, you need to actually feel the air to be sure the compressor is locked in.

I did think about using the Brisk Air evaporator to save some adaption, but since the old compressor had burned out and trashed the refrigeration system I did not want to introduce it into a clean environment. That's the junk that stops up cap tubes! As it worked out, the plastic mounting pieces from the Samsung evaporator and fan fit into the existing framework of the Brisk Air nicely.

Posted By: Lt46
on 09/30/08 08:20am

I love this type of innovation. I especially like it when the question "I wonder if this will work" pops into your head and you see it through to success. Good work Professor!

On the other hand why not just put the "window" A/C's compressor in the dometic unit...??

Posted By: professor95
on 09/30/08 08:26am

Bumpyroad wrote:well, it sort of seems like professor95 had no real problem with my comment, although you evidently did.
bumpy

Bumpyroad wrote:nice job. I bought a second air for my previous MH that was smaller for the reason that you stated. But good grief that looks like lots of work to save a couple of hundred dollars at most.
bumpy

itsalleasy wrote:You really don't have a clue why people do things like this, do you?

Come on guys, life is too short to expend our time and energy on who has a problem with what. Everyone is different and entitled to their own feelings and opinions - Sniping at each other about the differences is not going to change anything . I respect Bumpy's opinion, even if I may feel differently - enough said?

Posted By: professor95
on 09/30/08 08:37am

wwest wrote:On the other hand why not just put the "window" A/C's compressor in the dometic unit...??

I thought about that too. If I had a "clean" Dometic refrigeration system I might have tried it. But, I would have still had the larger and noiser fan from the Dometic and most likely would have needed to experiment with the capillary tube legenth to get the right temperature/pressure drop for the evaporator. The Samsung compressor has less volume per stroke and "may" not have supported the evaporator from the Dometic. Anyway, it is an interesting thought and one I would not mind experimenting with.

Posted By: Chris Bryant
on 09/30/08 10:49am

If you really feel like experimenting- I've always wondered about putting a TSV valve in a rooftop A/C, instead of those stupid cap tubes.

Posted By: quabillion
on 09/30/08 11:44am

Chris Bryant wrote:If you really feel like experimenting- I've always wondered about putting a TSV valve in a rooftop A/C, instead of those stupid cap tubes.

When I post my A/C projects You will be pleased to see that they ALL are upgraded to TXV (thermostatic expansion valve).
Heck one system will even be a dual txv!

Posted By: professor95
on 09/30/08 07:10pm

Chris Bryant wrote:If you really feel like experimenting- I've always wondered about putting a TSV valve in a rooftop A/C, instead of those stupid cap tubes.

OK, another story.

In the late '70's I had a Skamper PUP with an ice box. I decided to convert it into an electric refrigerator. I had a working dehumidifer that I did not need. I made a copper coil for the inside of the Ice Box and put it all back together with the compressor in an adjacent cabinet and the condenser under the PUP. It took several trys to get the cap tube the right legenth for the new evaporator coil to cool to 35 degrees, but I finally got the thing to work as a fridge. Of course, back then a can of R-12 was $.99 and no one even thought twice about venting it into the atmosphere. Now the only R-12 available in the USA is recycled and a 20# cylinder sells for $600.00. Amazingly, I ran across a box with six 14 oz cans of R-12 at a yard sale last spring. I gave the lady her asking price of $2.00.

Posted By: portablevcb
on 10/01/08 03:51pm

Love this job!! What's better than the idea is the execution. When I first started reading I thought it was going to be some home made duct work to route the air inside. Brilliant bit of work.

We kinda did it the 'bailing wire and duct tape' method on our old MH. Open the sliding portion of the window and remove screen. Make a window mount for the A/C unit and use 1/4" plexiglass to fill the rest of the space. We did have to remove it when traveling, but, only used it once a year anyway.

FWIW, the reason we did it was so we could 'hook up' to a std outdoor 120V outlet without popping the circuit breaker (when parking in the in-laws driveway). The 5k unit was enough for night time cooling in southern NM. The factory roof unit (an OLD 13k unit) would pop a std outlet circuit breaker.

I do like the idea of being able to run off batteries as well as the difference in noise.

Question. After taking both apart do you think the 5k unit will stand up to road travel as well as the factory unit? I had a bad experience with a home refer in an RV, ie, vibration killed it after a few trips.

Many of us just love using our tools to do something different. It's like "Why climb mountains?" and the answer is "Because they're there".

Of course this , also, doesn't make sense to many - but to those of us who are tired of posts debating the twinning of 2 Hondas, 6V or 12V batteries, inverters, inverters, inverters, etc. - this is a highly refreshing post. And with great pictures, too!

Thanks, Professor,

Harry Havasu

Posted By: Diabs
on 10/02/08 12:26pm

I just love DIY projects....I did the redneck version of this with a 5000btu in the window of my old trailer. It was the best $80 bucks I ever spent. My DW thought so too! when we stayed in Sugarloaf Keywest with the 100+ temps.

Your reasoning for a smaller unit was flawless (ie exactly what I would want)

I too am curious as to the power consumption figures. One would expect them to be exactly the same as the stock Samsung but it would be nice to see actual values.

Cheers,

O

Posted By: professor95
on 10/02/08 07:26pm

Pilotcamper wrote:Very nice!

Your reasoning for a smaller unit was flawless (ie exactly what I would want)

I too am curious as to the power consumption figures. One would expect them to be exactly the same as the stock Samsung but it would be nice to see actual values.

Cheers,

O

I can do that. I cut the NMC cable in the basement that runs from the circuit breaker to the new A/C and installed a plug on the end going to the A/C and an outlet on the end going to the circuit box. I did this so I could easily disconnect this A/C from the trailer's power and plug it into a small genny or inverter.

I also happen to have a Kill-A-Watt meter. It will be easy to collect the data you would like to have.

I'll let you know in a few days - or as soon as the WX in Virginia gets a littler warmer again.

Posted By: jauguston
on 10/03/08 09:06pm

Well - I started to build a unit like Randy built today.

I was given a Coleman Mach Roof AC that was dead by the local RV shop - YaHoo - good start. I went to Lowes and bought the same window AC that Randy used.

This afternoon I disassembled the Coleman down to the pan and cleaned it up. This evening I started tearing the Samsung apart and began to see a possible issue. I went ahead and removed all the covers and took a good look. Houston - We have a problem (-:

I don't know the correct terms but the radiator that the heat comes off of to atmosphere is 12" tall in the Samsung and 9" tall in the Coleman. S**t!!! This is going to hold the plastic cover 3" at least higher than it is supposed to be. The Dometic must be taller.

The shop had 4-5 AC units there but none were Dometic Breeze Air's.

Tomorrow I am going to try a couple of other RV shops in the county and see if I can find a Dometic. If I can't I will have to figure out how I can make the Coleman look right with the cover raised 3". Darn It. Shucks.

Jim

Posted By: MrWizard
on 10/03/08 10:43pm

maybe you have enough space to place the 'rad' ( condenser OR evaporator ) on an angle so it slopes ?

Options, always have options, and the journey goes much smoother....

Connected thru Verizon with HotSpot WiFi using a Samsung Galaxy Nexus

Posted By: quabillion
on 10/03/08 10:56pm

MrWizard. You took the words right out of my mouth

As long as all the air goes thru the `rad` it should be just fine.

Posted By: C Schomer
on 10/03/08 11:17pm

Your conversion came out looking really good! I like doing that stuff, too. I replaced a 13.5 Briskair on a fire dept. vehicle at work this week and the plastic cover was still in great shape cuz it's parked under a cover all the time. My old 15k Dometic cover on my 5er is like an eggshell but it has a shallow pan and I'm going have to change to the deep pan from the old 13.5 that I changed out in order to use the good 13.5 cover. Somebody suggested putting the 6k btu compressor in the 13.5 unit but that would be too much of a mismatch. A little bigger coils would be good but 13.5 is too much. Something like a 13.5 compressor in a 15k unit would probably make a really efficient unit with some captube tweeking.
For you guys that changed to a TXV... Did you add a sightglass or did you go by liquidline temp and charge by subcooling? What is the temp rise across the condensor after you charge the system enough to get some subcooling? Craig

For you guys that changed to a TXV... Did you add a sightglass or did you go by liquidline temp and charge by subcooling? What is the temp rise across the condensor after you charge the system enough to get some subcooling? Craig

I believe this is directed to me, correct? As I am the only one who said my project contained TXVs.

The proper way to charge the system using these particular valves is by subcooling.

My systems will also not be using R22 anymore. The valves that I have are intended to be used with R12, so I will use one of the many newer "enviro friendly" azeotropic blends. Most likely R414b. Or R409a

The reason for this is also to have a much lower head pressure. Thus the compressor will draw less power, because it has to pump up to only 160 psi instead of R22's 350+ psi.

And yes I am aware that R414b has a lower latent heat per pound than R22, and I am making provisions to account for this.

Posted By: Old & Slow
on 10/04/08 07:33am

All you Pros make for good reading but sadly I'm a novice. Prof, please post some 1-2-3 photos with a picture of the baffels needed. Or maybe this might be to involved for O & S? I want to add this unit for use with the possible use of a DC/AC Inverter and more silent night time cooling.

Floyd

Posted By: jauguston
on 10/04/08 09:54am

After sleeping on my problem of too tall a condenser for the Coleman I wonder if there would be a problem using the condenser from the Coleman. It has more area for sure but would that cause a problem.

I have a good friend that did all the AC work at the Georgia Pacific pulp and paper mill here for 40 years before they shut it down. He has all the tools pumps and what ever is needed it work on this stuff. He has lots of R-22 and probably 150 lbs of R-12. His boss told him to take all of it when they shut down so GP didn't have to pay to dispose of it. He obliged them (-:

I will ask him what he thinks of using the Coleman condenser but there is a lot of smart people here and any advice would be appreciated.

Would it work better if we filled it with R-12 or would it not work at all?

Jim

Posted By: quabillion
on 10/04/08 10:30am

jauguston

As one RVer to another, I am concerned here.

Do you have the proper licenses to be doing this type of work???

If one is caught by the EPA handling/using refrigerants without a license the fine can reach to $25,000, per infraction.

So between you and me, be careful what you post on a public forum.
Happy campin.

Posted By: C Schomer
on 10/04/08 11:06am

Thanks, I thought there were two guys that used TXVs. The reason for asking those ?? is because I'm wondering how the cond coil size works out. The advantage of a TXV is to fill the coil faster and pull the load down faster but a captube does fine on the superheat after the unit runs for awhile and stabilizes. A captube system doesn't always have 100% liguid at the cond outlet but a TXV HAS to for it to work it's best. So I'm just thinking that if you can't get the subcooling necessary for proper TXV operation at a reasonable head pressure and DT, the results might be really minimal - what you gain in evap efficiency will be lost in cond efficiency. I think I'd add an extra loop of soft copper at the inlet and outlet of the cond coil. I used to do mostly lo-temp refrigeration but I've been stuck mostly in an R22 world (up to 120T RTUs) for the last 30 yrs so I don't get much experience with the new refrigerants except for some small 404a, 134a and now a few 410a package units. We still even have some 11, 12, 500 and 502 around the power plant. From what I've seen, the new refrigerant compression ratios are similar to the old ones but the coils are much bigger. The thing that is really interesting is that they can't get the simple eer up anymore so they are improving the controls big time to get higher seer's. The ECM motors are fabulous and I see Maytag has a variable speed compressor now - 24 seer! I wonder if they use an ECM comp motor. Craig

* This post was
edited 10/04/08 11:18am by C Schomer *

Posted By: qtla9111
on 10/04/08 11:25am

I downsized our 13.5 by installing a Polar Cub. That was a waste of money. Fortunately I recovered 250 dollars by selling the old one to a woman who came by at the time they were changing it out and had been looking for a cheap air option.

Last year though, I tired of the loud noise, vibration and droning of the roof air. It was still too cold to sleep comfortably so I bought a 5000 btu a/c and made a cut out for the large window on the side of the bed. I can take it in and out in less than 5 minutes and the cut out fits under the bed.

The difference is day and night. Quiet, cools beautifully and most of all it can run up to 14 hours on a 1.1 gallon tank of gas, on econo mode, with my Honda 2000 generator. Best thing I ever did.

There is a method to the madness, disturb the method and the madness begins.

Posted By: quabillion
on 10/04/08 01:30pm

C Schomer wrote: A captube system doesn't always have 100% liguid at the cond outlet but a TXV HAS to for it to work it's best. Craig

A device known as a receiver at the outlet of the condenser coil is used to ensure that the valve is fed with 100% pure liquid.

In order to work properly, 99.9% of all the TXVs require pure liquid.

If you really want to learn the in and outs of all types of refrigeration, I suggest you go and buy the textbook for a college level HVAC course. Most places you dont have to be a student just to buy the book. Expect to pay around $60 bux for this 3 inch thick book, but it is well worth it IMHO.

I still have all 4 of my textbooks, and refer to them almost once a week.

Posted By: Chris Bryant
on 10/04/08 01:58pm

quabillion wrote:

I still have all 4 of my textbooks, and refer to them almost once a week.

An electronics instructor once told me "You don't need to remember all of this stuff, you just have to remember where to look it up".

Posted By: jauguston
on 10/04/08 02:17pm

Ryan, reread my second paragraph of the last post. The fellow that will do all the handling of refrigerant has been licensed to do that work for over 40 years and made his living at Georgia Pacific doing nothing but refrigeration and AC maintainance before he retired. He keeps all my vehicle airconditioning working well. He works part time at home now.

He told me once he was respossible for over 25,000 gallons of R-12!

Jim

Posted By: quabillion
on 10/04/08 04:09pm

Sorry jaugnston, I became confused between you and C Schomer.

They have had this license law ever since 1994-5 IIRC. Prior to that anybody could do AC work, and release freon to the atmosphere legally.

Your friend knows what he is doing, of this I am sure.

To Everyone; Doing this type of work without proper licenses is ILLEGAL in the USA.

There, now I'll just hop down from my soapbox.

* This post was
edited 10/04/08 04:15pm by quabillion *

Posted By: C Schomer
on 10/04/08 06:22pm

Quabillion, I almost asked if you added a reciever. So, did you measure the cond. DT and how many degrees over ambient is the saturation temp.? Craig

Posted By: jauguston
on 10/04/08 06:49pm

Here is the next installment on Jim's project.

After reading the suggestion to try leaning the condenser I thought that might work --- until I went out to the shop with my trusty tape measure --- No joy. The fan is 11 1/4" in diameter. The more I look at the Coleman Mach the more I believe it is just not a good candidate for this project.

I haven't been able to find the dimensions for the Dometic Brisk Air online but looking at Randy's pictures It must be about 12" high as the top of the evaporator shroud is 12".

I will start searching tomorrow for a Brisk Air. Darn It!!

Jim

Posted By: quabillion
on 10/04/08 07:59pm

C Schomer;

My A/C projects have yet to be completed.

I promise a thread with a highly technical description and explanation of theory involved. To answer all of the type of questions that you raise.

quabillion wrote:

When I post my A/C projects You will be pleased to see that they ALL are upgraded to TXV (thermostatic expansion valve).
Heck one system will even be a dual txv!

Posted By: Starman97
on 10/05/08 08:51am

quabillion wrote:

My systems will also not be using R22 anymore. The valves that I have are intended to be used with R12, so I will use one of the many newer "enviro friendly" azeotropic blends. Most likely R414b. Or R409a

The reason for this is also to have a much lower head pressure. Thus the compressor will draw less power, because it has to pump up to only 160 psi instead of R22's 350+ psi.

And yes I am aware that R414b has a lower latent heat per pound than R22, and I am making provisions to account for this.

Have you looked into using HFC-152a (CAS #75-37-6) ?
I'm using in as a replacement for R12 in my cab AC system, it works just fine there.

Posted By: Old & Slow
on 10/05/08 11:13am

My guess is that 'Converting a Window A/C to a Rooftop unit' is for Pros like Prof' to show another one of a kind, project for a real Pro. That leaves me out of the mix once again. Maybe some day a project will be shown that might apply to a old novice. Metel working has never been my strong suit even tho I like to try at times. But being a A/C tech, I am not. No license or licence. I hate being left out of the game, makes me sad.

* This post was
edited 10/05/08 03:26pm by Old & Slow *

Posted By: portablevcb
on 10/05/08 11:45am

But, it is not just for pros. You can do just about everything Prof did without breaking the lines open. You would have to be careful about bending so you don't break them, but, it can be done. The rest is metal work on the ducting and mounting the individual elements.

The problem would be as in Jim's case where the salvage RV unit is not sized for the window AC components.

charlie

Posted By: quabillion
on 10/05/08 01:39pm

Heck, Old & Slow.

I sure do hate to see my neighbors sad.

If you ever do decide to try and tackle an A/C project, let me know.

I would be more than happy to assist you in your project with my knowledge/license/special tooling.

Posted By: quabillion
on 10/05/08 02:04pm

Starman97;

No, I am not familiar with that particular refrigerant.
I will research and evaluate it.

I frequent the Austin area quite often to visit family and friends (I was an Austinite for 4 years before moving into the RV life)

I sure do miss those days of spending 11+ hours a day on my jetski out on lake Travis.

Turns out to be QUITE a workout, but its the best fun to be had legally.

Posted By: Old & Slow
on 10/05/08 03:50pm

quabillion wrote:Heck, Old & Slow.

I sure do hate to see my neighbors sad.

If you ever do decide to try and tackle an A/C project, let me know.

I would be more than happy to assist you in your project with my knowledge/license/special tooling.

Thanks Ryan,~aks 'off the grid'

Hey, home boy, I like the roof of your rig. Solar,well, you are 'King of the road' don't need no fifty cents for the grid or trailer park. You may get a PM from O & S some day to please help. I'm a PRO at being a tight wad. I like the idea of a 5000/6000 btu Chinese (Samsung) import for around a hundred bucks and a free (if possible) Brisk Air shell. Can I figure on the possibility of only adding baffels to complete the unit?

Floyd

Posted By: professor95
on 10/05/08 05:47pm

jauguston wrote:Here is the next installment on Jim's project.

After reading the suggestion to try leaning the condenser I thought that might work --- until I went out to the shop with my trusty tape measure --- No joy. The fan is 11 1/4" in diameter. The more I look at the Coleman Mach the more I believe it is just not a good candidate for this project.

I haven't been able to find the dimensions for the Dometic Brisk Air online but looking at Randy's pictures It must be about 12" high as the top of the evaporator shroud is 12".

I will start searching tomorrow for a Brisk Air. Darn It!!

Jim

Jim, I am really, really sorry I did not make the case part clear. I looked at the Coleman case as one was available. It was too flat and the cap did not bolt directly to the pan like the Brisk Air.

You will need the taller Dometic case.

Some folks have asked for specifics on the Samsung model I used. Below is a photo of the box. I learned something new about the unit this weekend; it has a “dry” function which is basically a dehumidifier that does not drop the temp much. This might be a real plus as the weather cools and moisture builds up inside the camper.

Posted By: professor95
on 10/05/08 09:36pm

I never dreamed this project would create the interest that is apparent. Evidently the RV air conditioner manufacturers are missing a significant part of the market by not offering smaller BTU units.

I did not intend for my sharing of this project to be a step-by-step guide. I now wish I had made more photos and documented the steps in more detail. I am reposting some of my previous images with labels so that most of the parts I reference can be identified.

The points I am listing below are for those who want to do a similar conversion. They will most likely not make any sense unless you have an old Dometic Brisk Air and the Samsung side-by-side. Therefore, you might want to skip all the reading unless you are contemplating doing the project.

Please, if you attempt this project you do it at your own risk! I cannot promise your project will work as mine did. I cannot promise my directions are 100% accurate. I cannot assure you that you will not be hurt doing the project. Again, any thing you attempt is at YOUR OWN RISK! Got it?

Keep in mind that I am writing this from memory – a dangerous practice considering that I can’t even remember where I laid my glasses!

You will need the usual assortment of screwdrivers, an electric drill with bits, at least one pair of Aviation Snips, a hammer, maybe a grinder and saber saw, a 13mm socket for the Samsung compressor nuts, gloves for protection, safety glasses, a tube of RTV (white?), a file, 1/4", 5/16” and 7mm nut drivers, pencil, tape measure, scissors, wire stripper, pliers, several 3” “L” brackets, butyl or similar sealing putty, 16 AWG wire, wire nuts, electrical tape, #8 x 1/2” self drilling hex head sheet metal screws, a 1/4” driver bit and extension for your drill, JB Quick Weld Epoxy and METAL FOIL DUCT TAPE – the GOOD STUFF! Some gray enamel spray paint to redo the base and perhaps some Krylon White for Plastic spray for the shroud if it is faded. I probably forgot something – but at least you have a list of the basics to collect.

When you strip the Dometic it is NOT necessary to open the sealed refrigeration system. If you do not have a license or recovery equipment please do not just cut the lines. The static pressure on the lines is around 125 PSI. What comes out will also contain oil and possibly pieces of a burnt out compressor. You can be seriously injured by opening a system without proper equipment and knowledge.

You can easily remove the Dometic evaporator, compressor and condenser as one assembled unit. Most localities have a recycling center that accepts refrigeration units with the CFC intact. They will remove the gas safely and properly to protect the environment.

I completely stripped the Dometic of all parts. I kept and reused the plastic pan that goes under the evaporator and has drains on each end, the front ducting that serves as the return air path from the air box and the circular enclosure the evaporator fan resides in along with its companion front plate. This front plate is removed by bending the retaining tabs up. Everything else got tossed.

The Samsung was completely disassembled. Before any wiring was disconnected a drawing was made of the connections, wires were marked, the capacitor was marked and digital photos were made. You should also note how far the condenser fan goes into the plastic shroud on the back.

The Samsung evaporator, compressor and condenser can be removed as one unit. They do not need to be opened and separated. You WILL need to expand the distance between the evaporator and condenser a small amount. There is more than enough copper tubing to allow this. The aluminum fins on both the evaporator and condenser are as sharp as razor blades. They are also extremely fragile. Again, be careful.

On the Samsung, the evaporator mounts into a piece of black plastic. This will be reused, but the bottom or drain pan of this plastic piece will need to be cut off.

Both the evaporator and condenser fan on the Samsung will need to be removed. The nut that holds the evaporator fan on has left hand threads. The condenser fan retainer nut has right hand threads.

Once the fans are removed, the motor can be removed by removing two mounting screws.

The plastic piece the Samsung fan mounts on is cut down in a circular fashion about 1” outside of the motor mounts. I used a band saw – the same one I cut my left little finger off with last year. A coping saw or saber say may also be used. BE CAREFUL!

The remaining plastic piece the fan motor mounts on is now bolted to the outside back of the Dometic circular shroud that forces cold air down into the square opening. Do this carefully so it is perfectly centered. Be sure the nuts are on the outside so the fan will not hit them. I used size 6 nuts, bolts and washers. The fan motor can then be remounted.

The next part is a little tricky. When the squirrel cage fan is placed back onto the motor shaft for the evaporator it is going to rub the back part of the Dometic shroud. It must be spaced out almost 1/4”. To do this you will need to remove about 1/4” off of the end of the plastic part of the fan that slides onto the motor shaft so the left hand nut can be put back on. The tricky part is on the inside – the motor shaft has a flat with a shoulder to keep the fan from going in too far. This flat must be extended about 1/4". You can accomplish this extension with JB Weld Epoxy. I put a small blob of the epoxy on the flat of the shaft, let it cure and then filed it so the shoulder was about a 1/4" higher than original. Keep in mind this 1/4" is relative – you may need more or less distance. What you can NOT do is put washers on the back side of the shaft to hold the fan out. Washers will bind against the motor bearing plate – not good. Check to be sure the fan spins easily without hitting anything. If it hits or scrapes, further adjustment as above may be needed. Once all looks good, put a drop of thread locker on the shaft threads and put the nut on hand tight.

Take the front metal piece of the Dometic fan shroud and put it back onto the fan housing. Bend the tabs down to secure it in place. Center the front plastic piece you removed from the Samsung over the opening of this metal piece. Bolt it on with 3 or 4 nuts and bolts as you did with the motor mount.

You may now secure the Dometic fan housing back over the square cold air outlet.

Carefully place the Samsung evaporator into the original plastic mount you have on the front of the Dometic fan shroud. With the other fan on the back of the motor, position the condenser with the OEM plastic shroud so that it does not rub. You can make fine adjustments later; right now you are doing this to determine where the compressor will mount.

Mark the position of the three holes for the compressor by poking a pencil down into the rubber mounts.

Completely remove the Samsung evaporator, compressor and condenser again – set them aside.

Drill three 3/8” holes in the Dometic base where the compressor will mount.

Retrieve the original Samsung metal base pan. With considerable finesse and care, you can cut the welds that hold the OEM compressor mounting bolts out of the pan. I used a 4” grinder with a cut off wheel and went around the bolts from the very bottom (outside). I then placed a nut back over the bolt so it was exactly even with the threads and whopped it with a brass hammer to knock it out. After the bolts are removed, clean off excess metal so they will fit flat into the Dometic housing. In case you are wondering why it is necessary to spend so much time moving the OEM compressor bolts it is due to the shoulder design. The depth of the shoulder is set to allow the compressor to be secured but not cause unpleasant vibration.

You may now mount the evaporator, compressor and condenser. Some “L” brackets will need to be added to the plastic condenser shroud for support. You will also need a top spacer/brace plate. I used the original Dometic top plate cut off from the top of the Dometic condenser shroud. This is where the fine adjustments are needed to be absolutely sure nothing is rubbing or hitting. Everything must be perfectly square and straight. Use thin metal shims under the condenser if necessary.

While the original Samsung condenser just friction mounted into the plastic holder, I added a couple of sheet metal screws to the edges.

Standing in front of the air conditioner, you may now replace the left hand wall for the return air box. Modification of this piece is not needed. The right hand wall will need to be cut so it will slip over the copper tubing going to the evaporator. This cut need not be perfect – just close. You can seal any gaps later with foil or rubber tape.

A piece of sheet metal approximately 12” x 6” will be needed to fill the open space on the left between the wall for return air duct and the front of the evaporator fan shroud. Bend it along the 12” length into a “L” over the edge of a board so one side is 2” and the other 4”. You may attach this piece with foil duct tape. You may reattach the top of the return air box now, or wait until the last step.

Use the metal foil duct tape to seal all of the air gaps and joints. Please DO NOT even think about using cloth duck (duct) tape – it is not worth a flip for ducts!

All that is left is the electrical work. I used a “knockout punch” to cut a 1” hole to the left of the fan motor thru the Dometic base (your left facing the front). Thru this hole I was able to pull the fan wires and connector. The capacitor was glued base down with RTV next to the hole I made topside. Wires were spliced and lengthened as needed to reach the control module on the air box.

At this point, I connected the control module and powered up the A/C on the workbench. One last fine adjustment to the position of the condenser was needed to get rid of the fan rubbing.

The sensor for the air temperature control is placed in the return air path, NOT the cold air box. I just plugged mine into the control module board and left the bulb end loose. When I installed the foam filter for the air box I placed it in the center of the pad.

I bought a new air box (see previous photos) that included an analog fan and temp control. They were removed and not used. You can see from the earlier photos how I cut the air box to accept the module. I glued it in with white RTV and let it cure overnight. The air box kit also included the cold air tube extension, mounting plate and long mounting bolts. The rooftop gasket was extra.

You can look at the previous photos to see how I got the thing on the roof. Once in place the long bolts are inserted thru the mounting plate inside the camper and torqued to 8 foot pounds. Electrical connections are completed. I used a Butyl putty to fill the hole the wires came thru, being careful to be sure the wires were not rubbing against the metal edges of the hole. Since the top of the control module is no longer encased in a protective metal box you should be aware that it is possible to get a real shock if you stick your hand onto the module from inside (this would take some work to do). Always flip the circuit breaker before messing around in this area.

* This post was
edited 10/05/08 09:54pm by professor95 *

Posted By: Bumpyroad
on 10/06/08 05:17am

professor95 wrote:

jauguston wrote:Here is the next installment on Jim's project.

After reading the suggestion to try leaning the condenser I thought that might work --- until I went out to the shop with my trusty tape measure --- No joy. The fan is 11 1/4" in diameter. The more I look at the Coleman Mach the more I believe it is just not a good candidate for this project.

I haven't been able to find the dimensions for the Dometic Brisk Air online but looking at Randy's pictures It must be about 12" high as the top of the evaporator shroud is 12".

I will start searching tomorrow for a Brisk Air. Darn It!!

Jim

Jim, I am really, really sorry I did not make the case part clear. I looked at the Coleman case as one was available. It was too flat and the cap did not bolt directly to the pan like the Brisk Air.

You will need the taller Dometic case.

Some folks have asked for specifics on the Samsung model I used. Below is a photo of the box. I learned something new about the unit this weekend; it has a “dry” function which is basically a dehumidifier that does not drop the temp much. This might be a real plus as the weather cools and moisture builds up inside the camper.

I had a window AC once with a "dry mode" which was merely a rubber nipple on the drain in the bottom so you could pull it down and instead of evaporating the water off it would just drain it. Set the thing over a floor drain, pull the nipple down, and run it. made cold air, pulled moisture out, drained moisture into floor drain, and put hot air back into room. was just a massive dehumidifier.
don't know how your "dry" function would be different?
bumpy

Posted By: jauguston
on 10/07/08 01:57pm

I placed the evaporator in the same location as the original one. My thinking was the air flow would be more likely to draw from the whole surface of the evaporator if there was some distance from the fan opening. I was concerned if I put it close like you did the fan would draw mostly from the center and maybe not so much from the perimeter. I am just guessing here.

Something I didn't mention is handling the Samsung components all hooked together with tubes is a bit of a challenge. I have a small overhead hoist on a track over my work bench and I finally rigged up some stuff to lift everything together. It was a PITA until I did that. It would be easy with two people.

The frost on the tubing was from my current draw testing. I made the measurements for the baffles while it was in there and I am making them now out of 1/8" ABS plastic sheet.

Randy -You have a PM.

Jim

Posted By: qtla9111
on 10/07/08 04:48pm

Use of cabinet air conditioners are coming back in smaller units. My 2001 Trailmanor had a window unit built into a cabinet with a drain pan and an outside vent cover. Worked great, was quiet and no droning sound. So that was a 27ft long TT.

I would do the same thing to my current TT or new one if I knew how to cut a hole in the side without affecting the structure or wiring in the wall. 5000btus cools our 18ft wonderfully.

Professor95, you're right. The Dometic Euro units are very small but just an example that it is a matter of making the change. I agree with your post completely about oversized units. Thanks.

Posted By: professor95
on 10/07/08 05:48pm

David_NC wrote:I modified an 8,000 BTU window A/C for the bedroom in my bus conversion. Mine wasn't for roof mounting, though. I set mine up to mount in one of the luggage bays below the floor. The hot air blows down through the floor of the bay, and fresh air is drawn in through a grill I added to the bay door. The cool air blows through a section of flex duct and into the bedroom via a 6" X 12" wall register. Return air is channeled through a filter-grill to the evaporator of the A/C. This system is almost silent... no noise or vibrations from above since the unit is mounted almost 3' below the interior floor. It will cool the bedroom just fine on 90+ days.

I realize my info doesn't really add to the topic of modifying a window A/C for roof mounting, but it could easily be adapted to mount in the front compartment of a 5th wheel, cabinet of a travel trailer or motorhome, etc. I can see applications for home or shop use, too.

I would have never thought to use a window unit in a roof enclosure, but it's a great idea for days when it's too hot for one unit to handle or when dehumidification and a small bit of cooling are needed. Thanks, Professor!

A great idea provided you can maintain adequate air flow thru the ducting and the condenser vents to the outside. Obviously you have accomplished both. Sure would like to see some photos!

Posted By: David_NC
on 10/07/08 09:20pm

professor95 wrote:

A great idea provided you can maintain adequate air flow thru the ducting and the condenser vents to the outside. Obviously you have accomplished both. Sure would like to see some photos!

One thing that helps is that I have it wired to run the fan on high only. Low doesn't really do the trick and I was concerned about low air flow. As quiet as it is high speed really isn't a bother. I'll try to get a couple of pics tomorrow.

I have wrapped up the work on the conversion on the top side. I have the air box ordered from PPL and then I will do the wiring and install the control panel. I have a pretty well equipped home shop and it went quite well. It took a little time to wrap my head around what had to be done and after that it only took a few hours to do the actual work. Fortunately the coach is pre-wired for a AC at the rear vent location.

I baffled the evaporator with a piece of 1/8" ABS plastic. I attached it to the evaporator with small Nyties wrapped around the tube loops. Then aluminum duct tape on the edge joints. New foam seal around the lid and closed it up. now I wait for the air box for inside. Boy what a messy shop!!

Jim

Posted By: Old & Slow
on 10/09/08 08:10am

Jim,

Wow, I think your retro 'might'? fit my skills. Beautiful job and also the photos are great. The baffles are fine engineering. Anxious to see the completed installation photos. This project is a good match to your sound lowering enclosure. What's next?

Floyd

Posted By: professor95
on 10/09/08 08:25am

Old & Slow wrote:Jim,

Wow, I think your retro 'might'? fit my skills. Beautiful job and also the photos are great. The baffles are fine engineering. Anxious to see the completed installation photos. This project is a good match to your sound lowering enclosure. What's next?

Floyd

Floyd,
I started to make this comment when you shared that this was only for the "pros".

I never intended for this to become a step-by-step guide, but it is sort of heading that way with Jim jumping in to do the project as well. As others do the same, we may eventually have all kinds of data to share.

Anyway, other than the physical aspect of handling the compressor/condenser/evaporator removal as a single unit and repositioning, I KNOW you are capable of doing this project. Since Jim came up with the idea of using a small overhead hoist like he has over his workbench to lift the compressor while positioning the coils, the job became more manageable. Of course, two people is an excellent idea too.

You once told me you could not do flip toward a genny project and could learn nothing about electricity. You proved yourslf wrong, didn't you? Now, you are one of the more knowledgeable on sound abatement and genny enclosure cooling and are often asked for advice.

My take is that this could very well turn out to be an excellent winter project for you and by Spring you would be another "I done it" advisor. Go for it, I know you can do it! You have at least two on-line advisors to help you if needed now.

Posted By: jauguston
on 10/09/08 08:47am

Floyd,

This project as you guessed is a natural add-on to the EU in the box. The EU in the box has been working fine for over 400 hours so far.

I think this conversion was a little easier than Randy's as there are some slight differences in the Duo-therm Brisk Air unit I started with.

Most any well equipped home shop should have all the tools you need to do it. I used my TIG welder to tack the motor mount studs to the base but that wouldn't be essential. They could be left loose and held with a pair of plyers to tighten the nuts.

Here is a recent project I modified from a shorter single wheel "Load carrying vehicle extension" I build a few years ago. It is not considered a trailer so no license or registration required and does not come under the double tow restrictions. It is considered part of the Samurai.

The boat is a 1448 Crestliner Jon Boat. There is a 15hp outboard and a Min-Kota electric bow mount motor plus fishing stuff in the box under the boat. The pictures were taken in the rest area in Winthrop, Wa a couple of weeks ago on our way home from Steamboat Rock SP near Grand Cooley Dam. 54' overall length. Tows like a dream. The wheels swivel and it is connected to the Samurai at two points at the ends of the Sami frame. The Sami rear license plate is moved to a clamp on bracket attached to the boat transom when on the road. The black things on the boat transom are swing down dolly wheels. I made a dolly that connects to the bow eye so I can move it around on the ground and there is a little hitch on the back of the trailer to hook that dolly to to pull it out of the water. There is a hand crank boat trailer winch mounted under the front of the boat on the bunk structure cross member that is hooked to the transom from underneath to slide the boat up the bunks.

Jim

* This post was
last
edited 10/09/08 09:13am by jauguston *

Posted By: David_NC
on 10/09/08 09:20am

I was going to post some pics of my basement A/C modification / installation, but it appears there's no way to attach pictures into the actual messages. This is the first time I've encountered this on forum software since the late '90's! I don't have time to find a site to host the pics at the moment. I'll try to do it later, or if anybody has a site, I can email the pics to them. Thanks.

Posted By: Bumpyroad
on 10/09/08 10:38am

David_NC wrote:I was going to post some pics of my basement A/C modification / installation, but it appears there's no way to attach pictures into the actual messages. This is the first time I've encountered this on forum software since the late '90's! I don't have time to find a site to host the pics at the moment. I'll try to do it later, or if anybody has a site, I can email the pics to them. Thanks.

use http://tinypic.com/

Posted By: Old & Slow
on 10/09/08 11:37am

Prof,

I needed that uplift. Most of my past skills (if any) were in world shipping. Mostly the guy between ship owners and shore problems and operation. Old skills on the DIYS level come from High School shop and younger days of wreching it. I do feel if I can do it, anyone can.
These threads on RV.NET have been a life saver (saviour). You have been one to lead the way. Thanks for putting up with Old,Slow and cranky. Some times I need a attitude adjustment for lower altitude.

Floyd

PS: If and when I get started on the Window A/C to Rooftop retro I'm sure help will be needed with all the head bangers. May need a rubber room for the A/C.

Posted By: quabillion
on 10/09/08 06:43pm

OK got some photos from David to post here.
I dont have any descriptions.

Posted By: David_NC
on 10/09/08 07:31pm

quabillion wrote:OK got some photos from David to post here.
I dont have any descriptions.

Thanks for posting them. The first pic is of the unit in the bay. The sloped part in the right (front) is the exhaust air from the unit which is blown down and out through an opening in the floor. You can also see the flex duct from the evaporator up through the floor and out a wall register into the bedroom.

In the second (left of the picture, facing towards the back of the bus) you can see the return from the bedroom that leads to the intake of the evaporator. The square duct is fabricated from foil-faced closed-cell polystyrene (styrofoam) that's generally used for insulating under house siding. You can also see the high tech hold down strap used to secure the unit!

The third picture shows the intake for the condenser in the bay door. It's cut into the rub strips (large aluminum panels) that run the length of the bus. It's covered with stainless mesh salvaged from another MC-8 bus. I painted a louvered vent flat black to keep rain out of the intake. I used a similar intake for my generator on the other side.

This unit is an 8300BTU LG window unit installed in the third (rearmost) bay on the curb side. These bays are large - 8 feet across, 33 inches tall, about 54 inches front to back. The rear bay will also house the holding tanks, water and drain / sewer connections, power inlet, water heater, and a diesel furnace. I didn't use the electronic control panel for the A/C as it was wired to the unit with a ribbon cable that was a real pain to try to extend. All I needed to control the A/C was a standard digital thermostat with a fan on/auto switch. I connected the fan to run on high only, as I didn't want there to be an issue with too little air flow across the coils. This system is almost silent when running... both inside and outside. It's about as loud as the standard refrigerator in the kitchen.

Hopefully this will give somebody an idea of how to add a small, quiet, energy efficient A/C unit in a motor home, travel trailer, fifth wheel, or even at home. Total cost was under $150.

David

Posted By: Old & Slow
on 10/10/08 03:54am

After reading thousands of posts, they all proves to me~'true value is in the product' Some are shifting into gold and others see the value of saving by "Converting a Window A/C to a Rooftop RV unit" Us folks, we will survive. It's all about VALUE.

Floyd

Posted By: professor95
on 10/10/08 09:48pm

To David_NC:

An extremely inovative approach. Thanks to both you and Ryan for getting the pics on the forum. I believe RVers are some of the most talented people in the world. Necessity is the Mother of invention!

Actually, our 5th wheel would be a good unit for a similar project. The front basement has a large duct running thru it that goes to the bedroom. It would be easy to tap into. Unfortunately, I do not have additional large storage bays and a lot of my storage space would be taken up by a basement conversion.

One thing that has been implied, but not specifically said, is that window air conditioners really have not changed much in design since they were invented. Different brands are also basically similar with a single double shaft fan motor to run the evaporator and condenser fan. They still use type R-22 refrigerant and use a capillary tube to drop the gas pressure and temperature. Compressors have gotten smaller, lighter and more efficient but still remain sealed cans.

The roof top Dometic A/C used on RVs (and some boats) is really nothing more than a window A/C with an air diverter to make the cold air blow down rather than out.

If I should elect to repeat this project, I would like to try and convert the window unit into a heat pump - or perhaps find a used but working/repairable 13,500 BTU Dometic to convert.

Posted By: professor95
on 09/01/09 09:22pm

It has been almost a year since I did the window to rooftop conversion. During that year the little A/C has run, and run, and run....

It has just enough cooling power to keep everything nice and comfortable in the bedroom.

Another plus is my inverter with four 127 amp hour deep cycle AGM batteries will run the A/C for at least 4 hours with the compressor locked in. Longer if the unit cycles. When we are dry camping, it is hot and humid and quite hours require us to turn off all generators at 10:00 p.m., we can run the small A/C an additional 4 or more hours before the batteries drop to the cut-off point of 11 volts.

Anyway - it has continued to work and we have really enjoyed the benefits of having a small A/C in the bedroom.

Posted By: professor95
on 10/06/08 07:53am

Bumpyroad wrote: had a window AC once with a "dry mode" which was merely a rubber nipple on the drain in the bottom so you could pull it down and instead of evaporating the water off it would just drain it. Set the thing over a floor drain, pull the nipple down, and run it. made cold air, pulled moisture out, drained moisture into floor drain, and put hot air back into room. was just a massive dehumidifier.
don't know how your "dry" function would be different?
bumpy

I am not sure either, Bumpy. I intend to check it out further.

Typical home purpose built dehumidifiers have both the evaporator and condnser in the same room - thus no heat is really lost. They also have extremely large evaporator coils without fins and adjust the temperature of the coil around 45 to 50 degrees F so it will not freeze and form ice.

None of those features are apparent on the Samsung A/C.

I'm thinking "maybe" the controls allow the compressor to turn on for a minute or two to cool down the evaporator to below the dew point of humid air rather than depending on the thermostat. Air that passes over the evaporator will form condensation on the coil. Then the compressor turns off and the condensation drains into the drip pan and rolls off the RV roof. The compressor on/off cycle starts again.

It won't be hard to observe how it operates to learn. I just thought such a feature would be neat for an RV when I noticed the remote had a "dry" button and looked it up in the manual.

I spent most of one Virginia winter living in a camper back in '89 when I switched jobs (home was 140 miles from work). Moisture was a really big problem inside the camper during the winter. I remember waking up one night with water dripping in my face - it was condensation on the inside of the plastic roof vent over my bed. During one really cold period with temperatures in the single digits, the aluminum frame on my rear door actually froze indoor condensation so I could not even get it open!

I used a regular dehumidifer some. But the camper was small, the dehumidifer took up a lot of room and was noisy.

Last year I bought a really small dehumidifer from Wal-Mart for around $50 that used one of those electronic units with no moving parts - same thing they put in these electric coolers/warmers. It worked, but not really well enough to do a whole lot of good. It might help in a closet, but not in a camper.

Of course, most RV air conditioners will not even cut on the compressor if the outside temperature is below a set point - usually around 68 degrees. They are designed this way to prevent icing up the evaporator coil and burning out the compressor.

Posted By: Bumpyroad
on 10/06/08 08:07am

Reminds me of when I lived in the Cincinnati area in a house trailer. had a 10 x 10 bedroom. Cincinnati was horribly humid compared to what I was used to in KC, MO. the only way I could get comfy during the cooler weather was to put a dehumidifier in the bedroom and close it up. took moisture out, put heat in, ended up great.
bumpy

Posted By: Old & Slow
on 10/06/08 09:28am

Prof,

Thanks for the details on the retro Samsung/brisk Air A/C. I hope the details will be a great help for those who feel qualified to do the job. As for me, it looks to be more then I would be able to accomplish. If younger and bold, it would be a 'go to' project. Prof, you truly are a wonder to behold. A man of many talents.

Floyd

Posted By: jauguston
on 10/06/08 01:28pm

Life is good!!

I started out this morning with a list of 15 RV repair places I found in the phone book to see if I could find the Duo-therm Brisk Air unit I needed. They were within about a 50 mile radius of home. The second shop about 6 miles away had three of them and they gave me one. Yippee!!!

I just finished stripping it down after reading Randy's latest detailed description of what he did and how. Thank you Randy!!!

The process looks pretty clear and I really have no doubts I can "Git Er Done" (-:

The only potential problem I see is I may have to raise the flat roof I have over the MH to clear the unit. It looks like it will be about 4" higher than the Coleman I have up front. Not that bad to do though. I had to raise it 8" to fit this MH when we upgraded from a 27' class C.

Jim

* This post was
last
edited 10/06/08 03:54pm by jauguston *

Posted By: 'nawlins
on 10/06/08 01:57pm

I laid my canoe upside down, gently, on top of my '95-13.5 Duo-Therm on StarCraft pop-up for trip to camp grounds. Needless to say, due to long time UV damage, the covers will crumble like and egg shell.

I have kept pop-up covered over the years but, unlike the lucky few, I paid the $115 for new shell last month..ouch. No good used shells around my neck of the woods

Dark Green HD Dmax wrote:Kodos to U...Well Done! One bad thing now....the price of RV AC unit shells will SKYROCKET !!!!! & No more free used (scrap) units! If this catches on, the RV industry WILL figure an angle to get more profits from the retrofits...unless your redoing a unit you already have!

Posted By: jauguston
on 10/06/08 04:02pm

I have gotten the Samsung pretty much apart and now see the Samsung condenser fan goes into the Brisk Air housing. The Samsung fan is thinner than the Brisk Air one leaving a lot of gap between fan and housing. Should there be some kind of filler placed in the housing or will it blow enough as is?

I am beginning to notice some small differences between Randy's description of certain parts and what I am seeing. Probably slight differences in different models or age differences. Not anything that will be a problem.

Jim

* This post was
edited 10/06/08 04:42pm by jauguston *

Posted By: professor95
on 10/06/08 05:04pm

jauguston wrote:I have gotten the Samsung pretty much apart and now see the Samsung condenser fan goes into the Brisk Air housing. The Samsung fan is thinner than the Brisk Air one leaving a lot of gap between fan and housing. Should there be some kind of filler placed in the housing or will it blow enough as is?

I am beginning to notice some small differences between Randy's description of certain parts and what I am seeing. Probably slight differences in different models or age differences. Not anything that will be a problem.

Jim

I too pondered on the extra space. I was tempted to fill it with pieces cut from foam insulation board, which would have been relatively easy to do. But, when I fired the fan up for a blow test, I found the suction into the evaporator and the air flow down the cold air outlet more than adequate. Thus, I just left it alone.

Jim, I hope you are making digital photos and notes that you will share. Yes, I would imagine there are some model differences in the Dometic line.

One thing I did not share initally that maybe I should now. The cover for the A/C I was given was intact, but the top was warped and the entire thing felt sort of flimsy. I cut a piece of fiberglass matting, the stuff used for boats, the same size of the inside of the cover (just the top, not the sides). I laid the cover upside down on a sheet of smooth plywood. Using polyester resin, I coated the inside of the cover and laid the fiberglass mat inside. I then completely saturated the mat with resin.

Using a roll of Reynolds Wrap Release aluminum foil, I completely covered the wet and sticky mat with the foil. I laid three pieces of 2 x 4 lumber 22" long on top of the foil so that they were between the molded in ribs of the cap. I then set several cinder blocks on the 2 x 4 pieces to press the entire mass down.

The next day I removed the blocks and lumber. The foil pulled right off. The top was flat and much stronger than original.

I scrubbed the top down with a Mr. Clean Magic Erasure. It turned out so good I did not need to use the can of Krylon White for Plastic I had bought.

Posted By: qtla9111
on 10/07/08 04:20am

Dometic Europe makes both a 3500btu and a 4200btu roof air for European rvs. When asked if they would ever sell those here in the Americas the answer was no.

Posted By: professor95
on 10/07/08 09:39am

qtla9111 wrote:Dometic Europe makes both a 3500btu and a 4200btu roof air for European rvs. When asked if they would ever sell those here in the Americas the answer was no.

Those are pretty small units. Unless it was a well insulated van conversion, I can see why they would not be too popular.

I am not insinuating that you do not know the information contained in what I am about to write. You have just given me the opportunity to expand on the concept of using smaller A/C units and ultimately less electricity – teachers have a (bad?) habit of doing that!

IMHO (In My Humble Opinion):
We (Americans) have been trained to believe bigger is better. We are just now beginning to realize this just isn't so - primarily because of the loss of cheap energy and overcrowding.

Oversize air conditioners can be worse for more reasons than energy consumption. Air conditioners do not add cold to the air. They remove heat from the air. Until an air conditioner can remove the majority of moisture (humidity) from the air heat removal will be minimal.

We control most air conditioners by the use of a thermal sensor called a thermostat. Only the newer more complex electronic thermostats measure humidity as well as temperature. The conventional A/C thermostat only measures the expansion of a fluid or gas in a bulb that applies pressure to a membrane switch in a sealed assembly. The gas in the assembly expands when warm (or hot) applying pressure to the switch, when it cools, expansion is reduced and the switch pressure is released. This may be a good design for heating, but it is not for cooling – especially in climates where humidity is consistently high when it is hot (like where I live in Virginia).

Oversize air conditioners will cycle frequently due to the operational design of this type of thermostat. Thus, dehumidification may be inadequate. Smaller air conditioners, or better said A/C units properly sized for the space you want to cool, will not cycle as frequently and thus can do a better job of dehumidification. With a lowered humidity level, we will ultimately feel more comfortable. Of course, if you are in the middle of Death Valley and the humidity is 0% with the temperature 110+ degrees F, this theory gets shot to Hades. In that situation you want all the heat removal capacity you can get.

I guess what I am trying to say is suppose we have an RV with a 12x8x7 foot area to cool and calculations tell us 6,000 BTU will adequately cool the area. So, we go to the RV air conditioner store to buy a unit. Sitting on the shelf is a 6,000 BTU unit that is priced at $500.00. Next to it is a 13,500 BTU unit priced at $575.00. We typically reason that for $75.00 more we can get twice as much cooling capacity – never mind power usage, noise, weight or the ability to dehumidify. So, we buy “the deal”. After a while, the RV air conditioner store no longer carries the smaller units because no one is buying them. Next, the manufacturer quits offering them because the stores can’t sell them.

This is what I believe has happened to the smaller RV air conditioner market in our country.

In my case I could have easily set a second 13,500 BTU or even another 15,000 BTU on the hole in the roof over the bedroom on the 5th wheel. But, I would have required a 3,000 watt generator to run it if we needed a cool area on a hot day at a non-hookup site. The 3,000 watt generator would take up 3x the space a small 1,000 watt portable unit would – it would also cost at least 3x more. The 3K genny would weight 50 to 75 pounds more – adding weight that would make the TV burn more fuel when towing. I would also loose some valuable cargo space with a bigger genny. The 13,500 BTU AC would also weigh more than a smaller unit. This would add another 40-50 pounds to the camper weight and ultimately cause the TV to burn even more fuel. If we stopped at a campsite that only offered a 30 amp hookup, we would not have been able to run both big A/C units at the same time. I could buy an expensive cycle switch that would run one then the other – but why? With a smaller bedroom unit we can run both the 15K unit and the 6K unit at the same time off of a 30 amp hookup so we stay nice and cool throughout the RV on a hot day with a lower power requirement.

Now that I am on a roll, this brings me to yet another point I want to explore.

I have befriended a gentleman who owns a small campground we like to use as a relaxation get-a-way. He recently went up on his rates by $10 a night ($25 to $35). He told me he had to increase the rate because electricity use was way up. When our power company added an 18% increase to the old rate, he was loosing money. Why was electricity usage up? More rigs with A/C, more big rigs with dual A/C, electric water heaters, and careless conservation measures. People go off and leave their campers with everything on – lights, A/C, TV – the whole works. They think it makes no difference since they are not paying for the power. But they are!

I asked him why he did not just set a tiered rate and charge extra for A/C or multiple A/C units. He replied that people got upset with tiered rates; some ignored them and used electric water heaters and A/C units anyway. Many folks ran their air conditioners with the camper door open! It was best to just adjust the base rate.

So, what happened?

Well, with fuel cost up folks don’t camp as much. With campground cost up, folks don’t stay as long or just don’t go.

Add in the increased cost of getting rid of garbage, higher labor cost for workers, a 5x cost increase for pumping the septic system every few months (sewage treatment rates soared on the other end). Higher fuel cost for his tractor to mow and increased maintenance cost for the pool and bathhouse. The county he is in has reassessed his property and increased his tax rate to double what it was five years ago. Even with the camping rate increase he is still loosing money and can barely pay his bills (at least that is what he tells me).

I asked him what campers can do to make a difference. His reply was not to use so much electricity, clean up their campsite when they leave, don’t trash the bath house, respect the property and provisions he includes. He noted that so far this year five new picnic tables that cost in excess of $100 were destroyed by campers. His pumping of the septic system was more frequent (according to the septic guy) because folks were using too much formaldehyde stuff in their holding tanks. Thus, the septic system bacteria needed to break up waste could not survive.

Next year he will need to go up at least another $10. He knows that this will reduce the number of campers who come to his campground.

He is seriously considering just closing the campground and selling it off to a developer who will subdivide it into housing lots.

Some campgrounds are even charging an extra $5 for each pet per night – this irks the living daylights out of me! (we have a well behaved miniature Dachshund who camps with us) When I asked one campground (Emerald Isle, NC) why they charged the extra $5, I was told, “Because irresponsible pet owners do not clean up their dog’s poop. We also have more complaints we need to respond to from campers who get tired of dogs barking all the time. This takes additional manpower and wages which is why we charge extra for pets.” So, those of us who have pets, clean up after them and control their behavior have to pay for those who do not?

Wow, I did get on a roll, didn’t I? It did not start out that way – I just kept on typing and sharing my concerns. I am tempted to hit the cancel button and just dump this all into the recycle bin. But, this thread was about converting a small window A/C to a roof top unit for RV use. Again, the conversion was not about saving money over purchasing a new unit - it was about efficiency and conservation which has a trickle down effect in many other areas - some of which I just addressed.

Bottom line – we all need to be more responsible as campers or we will not have places to camp! I know, I am probably preaching to the choir – folks who read this are already responsible campers. It’s the “other” guy who causes the problems – right?

* This post was
edited 10/07/08 09:54am by professor95 *

Posted By: jauguston
on 10/07/08 12:16pm

I have taken a few pictures of my progress and now I will see if I can remember how to post them.

Here I have the components setting sort of where they go and have powered it up to see if everything clears.

I cut the slot for the condenser tubes with my angle grinder with a cut-off wheel. I will seal it with chrome tape.

I did not have to do the shortening Randy talked about on the fan. It is in its original location on the shaft.

This unit has three studs to mount the motor to. I cut down the plastic piece the motor was mounted to in the Samsung like Randy did and mounted it with those studs. I made a temporary bushing to fit the shaft and the hole in the housing to center things when I marked the holes in the plastic for the motor mount.

Now I will see if anything shows up (-:

I now have the Samsung parts back out and am installing the motor mount studs. I will tack weld each one in a couple of places underneath with my Tig welder.

I will make the baffles for the condenser to direct all the air through it. I will also make baffles to separate the exhaust heat from the evaporator from the incoming air to the evaporator fan.

I checked current draw. Fan only .65a - compressor and fan started at 3.2a and went up to 4a when I shut it off.

Now that I see this is going to work I will order the housing that goes inside.

The unit I have is Duo-Therm Brisk-Air Model 57915-531

Jim

* This post was
edited 10/07/08 12:38pm by jauguston *

Posted By: professor95
on 10/07/08 01:08pm

Jim,

The major difference I see between our two projects is the position of the evaporator. I placed mine about 1" from the fan intake. I believe you will be OK as long as you baffel around the evaporator so that air is drawn thru it and not around it. The ice forming on the evaporator in your photo is due to inadequate air moving thru the coil. Again, this is a must!

Its looking good!!!!! Yes, there are some visible differences in the Dometic parts - like the insulation around the fan housing and a wider filler piece. To me, it looks like you have a better unit for conversion.

Please keep up posted on your progress!

Posted By: David_NC
on 10/07/08 01:09pm

I modified an 8,000 BTU window A/C for the bedroom in my bus conversion. Mine wasn't for roof mounting, though. I set mine up to mount in one of the luggage bays below the floor. The hot air blows down through the floor of the bay, and fresh air is drawn in through a grill I added to the bay door. The cool air blows through a section of flex duct and into the bedroom via a 6" X 12" wall register. Return air is channeled through a filter-grill to the evaporator of the A/C. This system is almost silent... no noise or vibrations from above since the unit is mounted almost 3' below the interior floor. It will cool the bedroom just fine on 90+ days.

I realize my info doesn't really add to the topic of modifying a window A/C for roof mounting, but it could easily be adapted to mount in the front compartment of a 5th wheel, cabinet of a travel trailer or motorhome, etc. I can see applications for home or shop use, too.

I would have never thought to use a window unit in a roof enclosure, but it's a great idea for days when it's too hot for one unit to handle or when dehumidification and a small bit of cooling are needed. Thanks, Professor!